The Island Purgatory

Following his vision of the Afterlife Brendan is allowed to see this:

From the (outermost, C version; eastern, M version) face of a rock Brendan and his crew see burning birds (souls, M version) bursting forth. At the same time they hear a multitude of voices sob and sorrow. An unfathomable sea battles the rock, making noise that can be heard for miles. Then they see (acc. to C/H versions, coming from the mountain) an enormous flam which sends sparks up into the sky (and coals the size of masts). From the mountain black, boiling water runs down, which is so hot that the stones burst. From the other side of the rock issue water and wind, which are terribly cold. On one side of the rock, it is hot, on the other so cold that the bark comes off the tree-trunks. Brendan tells his crew to pick up their orars. It now takes them two years (C/H version; in the P version, it takes three days) to leave the place which they had reached in one day.

-- Clara Strijbosch, The Seafaring Saint